You perform spirometry with Helium Dilution on a male aged 56 years with a 40 ye

Question

You perform spirometry with Helium Dilution on a male aged 56 years with a 40 year cigarette smoking history of 2 packs/day. Patient complains of lingering cough and production of about 200 ml/day yellow sputum tinged with red flecks, mostly in the morning. You prepare the spirometer for the subject, then start him breathing from the instrument when he reaches the end of a normal tidal expiration (he starts breathing from the spirometer when his lung volume is FRC).

You record the following values:

Initial [He] in the spirometer (before the subject breathes from it): 5%

Final equilibrated [He] in spirometer (with subject breathing from it): 3%

Initial Spirometer Volume (before subject breathes from it): 6.6 Liters

TV = 0.8L

ERV = 1.5L

VC = 4L

Breathing Rate: 12 breaths/min

Calculate the following:

1. FRC (functional residual capacity) in liters

2. RV (residual volume) in liters

3. TLC (total lung capacity) in liters

4. IRV (inspiratory reserve volume) in liters

5. Total ventilation rate in liters/min

6. Alveloar ventilation rate in liters/min (assume deadspace volume = 150 ml)

If someone could please explain how they got their answer, that would be awesome!

Explanation / Answer

Based on the given data,

The calculation of Residual volume is:

1) The calculation of functional residual capacity by Helium dilution technique is as follows:

Subject rebreathing from a closed circuit with known initial volume (V1) = 6.6

Concentration of helium (C1) = 0.33 L (5%)

After a period of rebreathing, the final helium concentration (C2) is taken = 0.2 L (3%)

V1 x C1 = (V1 + FRC) x C2

FRC = V1x (C1/C2 -1)

FRC = 6.6 x (0.33/0.2-1)

= 6.6 x 0.65 = 4.29L

Thus, the FRC = 4.29 L

2) The RV (residual volume) in liters: Cinitial x V = Cfinal x (V + FRC)

0.33 x 6.6 = 0.2 x (6.6+4.29)

2.17 = 0.2 x 10.89

2.017/2.17 = 1L

Thus, the RV = 1L

3) The TLC (total lung capacity) in liters is: VC + RV

Thus, 4+1

5 L

4) The IRV (inspiratory reserve volume) in liters is = TV+ERV-VC

Thus, 0.8+1.5-4

= 1.7

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.